koitsu at FreeBSD.org
Sun Oct 12 08:43:38 UTC 2008
On Sat, Oct 11, 2008 at 04:21:55PM -0700, Nate Eldredge wrote:
> On Sat, 11 Oct 2008, Pegasus Mc Cleaft wrote:
>>> FWIW, my system is amd64 with 1 G of memory, which the page implies is
>>> insufficient. Is it really?
>> This may be purely subjective, as I have never bench marked the speeds, but
>> when I was first testing zfs on a i386 machine with 1gig ram, I thought the
>> performance was mediocre. However, when I loaded the system on a quad core -
>> core2 with 8 gigs ram, I was quite impressed. I put localized changes in my
>> /boot/loader.conf to give the kernel more breathing room and disabled the
>> prefetch for zfs.
>> #more loader.conf
> I was somewhat confused by the suggestions on the wiki. Do the kmem_size
> sysctls affect the allocation of *memory* or of *address space*?
The Wiki is somewhat vague and doesn't give you all the knowledge you
The kmem_* sysctls do not define pre-allocated amounts. They define the
amount of memory which can be used by the kernel for allocation.
I strongly advocate tuning two other sysctls, which can help greatly
in ensuring no system lock-ups and no kmem exhaustion panics:
The following values are what I use, but others have reported better
performance with arc_max set to 128M:
> It seems a bit much to reserve 1 G of memory solely for the use of the
> kernel, expecially in my case when that's all I have :) But on amd64,
> it's welcome to have terabytes of address space if it will help.
ZFS is a memory hog, period. That's just the nature of the beast.
You probably should not be using it on a system with 1GB. I'll remind
you that memory right now is *incredibly* cheap; you can get 4GB of
brand-name lifetime-warranty RAM for around US$40-50.
Secondly, with regards to amd64:
RELENG_6 and RELENG_7 amd64 cannot handle more than 2GB of kmem. Yes,
you read that correct; it's not a typo. It's an implementation issue
which cannot be easily solved on those releases. CURRENT can address up
to 512GB. I've fully documented this on my Wiki, see section Kernel.
| Jeremy Chadwick jdc at parodius.com |
| Parodius Networking http://www.parodius.com/ |
| UNIX Systems Administrator Mountain View, CA, USA |
| Making life hard for others since 1977. PGP: 4BD6C0CB |
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